The present invention applies to still cameras which use the commonly available disc film cassettes. Unlike the conventional roll type films, such disc film is packed in a cartridge or cassette of thin section. It is in the form of a flat circular disc which contains exposure frames symmetrically located about the center of the disc. On the periphery of the disc are notches, respectively located opposite the various exposure frames. The notches are used for frame positioning. Conventionally the disc film has been rotated from its center hub to advance it one frame length after each exposure.
Most still cameras currently available on the market have film-transport mechanisms generally classified into three categories. The first type is a mechanical device that requires the camera user to push a film-advance slide once (or more than once) or to rotate a film-winding knob in order to transport a fresh exposure frame into the imaging position subsequent to a previous shutter release. In addition to possible manual focusing and exposure settings, the camera user has to make two operations in order to take a picture, i.e. to advance the film and then to depress a shutter release button.
In the second type of camera, the film-transport mechanism is a spring-wind mechanism in which a strong spring must be pre-tensioned by the camera user by the rotation (typically several revolutions) of a spring winding knob. Such a mechanism can also be considered as a semi-automatic device because, during most of the time, only one operation is required by the user to take a picture (apart from focusing and exposure adjustments), i.e. to depress a shutter release button. Subsequent to each shutter release, the pre-tensioned spring releases a portion of its stored energy to drive the mechanism for film-transport. When the pre-tensioned spring has become slackened after several exposures it has to be rewound again by the camera user. Examples of such cameras are disclosed in U.S. Pat. Nos. 3,685,414 (Good) and 4,226,517 (Skarman).
In the third type of camera, an automatic film-transport mechanism is driven by means of an electric motor. Subsequent to each shutter release, the motor circuit is closed for film transport and then interrupted upon completion of transport. Such a system is very convenient to the camera user, who only needs to depress a shutter release button in order to take a picture. However, this system requires an external energy source usually supplied by batteries. In the event that batteries are not available, the camera is in fact inoperative. In the above three types of cameras, either the manual, the spring actuated, or the motorized types, the film-transport operation usually also functions to cock a shutter mechanism.
Moreover, the film cassettes as received from the manufacturer usually do not have the first frame properly positioned, the first frame being normally only half-way advanced to proper position for exposure. Thus, an initial half-frame film advancing operation is necessary by one means or another after cassette insertion. Although electric motor drive systems are known in the art for automatically actuating a film advancing operation upon closure of the film loading door after cassette insertion, the expense and complexity of electric motor drive systems, as well as their dependence on the state of the battery, all constitute detriments of one form or another. Thus, none of the above described film transport systems effectively reduces the number of operations necessary to advance the film without adding either extra steps or substantial system complexity and cost.
It would therefore be a useful contribution to the camera art to provide a simple, low cost film advancing system that would not require either a separate spring-tensing operation or electrically powered motors, and which would further have the capability of automatically positioning the first frame of the film properly upon cassette insertion without requiring extra operations by the user.
A fourth type of camera not currently being marketed satisfies some of these objectives. Such cameras provide a purely mechanical film advancement responsively to actuation of a single shutter release member (See U.S. Pat. No. 1,960,998 to Hindley et. al.). This patent discloses a roll film camera designed to be mounted on a barrel of a pistol, shutter actuation and film advance being secured by means of linkages to the trigger of the gun. The employment of disc film is not mentioned or suggested in this reference. The internal details of the Hindley camera are not shown; however, if one assumes that the film is to be dispensed from some form of rewind cassette, it is clear that film breakage can occur if the trigger is pulled at an end-of-film condition, since pulling the trigger not only actuates the shutter, but advances the film as well. To eliminate such breakage some form of slip clutch or other film advance disabling feature would be necessary to prevent this, thus adding to system complexity.
U.S. Pat. No. 2,625,087 (Steineck) describes a disc camera for a disc film cassette of a different type than that presently being marketed. This camera has a shutter operating member configured in the form of a lever, depression of the lever serving to cock and release the shutter and to rotate the film as well. A non-standard cassette is described, the cassette having a great variety of internal elements configured to interact with the shutter actuating system. The Steineck system, however, is quite complex. For example, it inserts a time delay between shutter tripping and film advance to prevent undue camera motion during exposure. Further aspects of this system will be discussed subsequently.
Thus, both of these patents disclose systems for securing film advance as well as shutter actuation automatically by actuation of a single operating member in a single squeezing or depressing motion.
Additionally, it would be a further contribution to the art if such a system could provide for a compatible system for insuring that the film, once advanced, is properly pressed against the framing shroud normally provided in such cameras, to ensure that the film is pressingly engaged against this generally planar element to position the film at the imaging plane of the lens. Such a system, however, must not be incompatible with the design objectives previously stated.
In addition to providing for a purely mechanical film advancing and shutter actuating system responsive to operation of a single member, there is a further need to provide for protection against breakage of the disc film should the user attempt to advance the cassette beyond the last frame. This problem arises because the commercially available cassettes have a built in locking mechanism that prevents the disc from further rotation beyond the last frame. As a result, it is necessary that any single-member actuated camera have provision for preventing actuation of the film advancing system after the last exposure has been made, so as not to apply a damaging torque to the film disc. Additionally, not only must the film advance be disabled, but shutter actuation must be disabled as well so as to prevent accidental double exposure of the last frame. Although automatic drive termination and shutter actuation systems are well known in the art in electrically driven cameras, merely requiring some form of end-of-film sensor actuated switch to shut down both systems, a simple purely mechanical realization of this feature would be highly desirable. Moreover, such a system should warn the user that further exposure is impossible without film replacement.